An organic EL (electroluminescence) panel includes an organic EL element as light-emitting element and is a self light-emitting panel that can be applied to various usages such as various indication devices, for example, as indicator display of cellular phone, monitor display for automotive and home electronic devices, information indication display of personal computer and television device, etc.; various light sources, for example, scanner and printer, etc.; lighting devices, for example, general lights, backlight for liquid crystal indication devices, etc.; optical communication device using opto-electronic transformation function, etc.
An organic EL element is as nature subject to deterioration of luminescence characteristic when in contact with water, etc. contained in the air. Therefore, a sealing structure is inevitable to block air from the organic EL element for a stable and long operation of the organic EL panel. As a generally adopted sealing structure for organic EL panel, a sealing member made of metal or glass and a substrate on which the organic EL element is formed are bonded so as to form a sealing space encapsulating the organic EL element to house a desiccant in the sealing space (hollow-sealed structure). Also, in view of still thinner panels or improved strength, an investigation on a solid sealing structure is in progress for coating the organic EL element directly with a sealing material without space.
According to the conventional art described in patent literature 1, there are included a first substrate including an organic EL element on the surface, a second substrate bonded with the first substrate, and a desiccant layer formed on the surface of the second substrate, wherein the surface of the desiccant layer is coated with a stress buffer layer made of a resin layer.    [Patent Literature 1] Japanese Unexamined Patent Application Publication 2003-317936
In the organic EL panel that adopted the above-mentioned hollow-sealed structure, the presence of the sealing space largely influences the thickness of the panel, requiring the gap of the sealing space to be made small. In such a case, a deformation of the substrate or the sealing member may cause the inner surface of the sealing member or the desiccant layer housed on the inner surface of the sealing member to come into contact with the organic EL element on the substrate.
A desiccant layer including a binder resin and a desiccant component of an inorganic material is used. As the desiccant component of an inorganic material is in form of particles or grains, microscopic irregularities are formed on the surface of the desiccant layer. Therefore, the organic EL element, when contacted by this surface, may be mechanically damaged, causing a deterioration that causes a luminescent defect such as leak. In the above-mentioned conventional art (patent literature 1), in order to solve this deterioration, the desiccant layer is coated by a stress buffer layer made of a resin layer such that the surface irregularities of desiccant layer do not directly contact the organic EL element.
However, in this conventional art, the substrate on the surface of which the organic EL element is formed (first substrate) is transferred from a film formation chamber to a sealing process chamber, while the sealing member on which a desiccant layer and a stress buffer layer that covers the desiccant layer are formed (second substrate) is transferred to the sealing process chamber via another atmosphere than the above-mentioned film formation chamber. Therefore, dusts, etc. may be adsorbed on the surface of the stress buffer layer during the transfer step. In such a case, disadvantageously, the adsorbed dusts, etc. may damage the organic EL element when the surface contacts the surface of the organic EL element even if a stress buffer layer provided.
In addition, in the above-mentioned conventional art, the desiccant layer is coated with a stress buffer layer made of a resin layer. Therefore, the moisture that has penetrated into the sealing space can only be absorbed through the resin layer. Consequently, the essential function of the desiccant layer to absorb the moisture penetrated into the sealing space may be lowered.
On the other hand, when adopting the solid sealing structure, a sealing adhesive layer contacts the surface of the organic EL element. In order to improve the adhesive strength and the strength of the entire panel thereby, filler may be mixed in the sealing adhesive. The surface irregularities due to the presence of aggregate contacts the surface of organic EL element and may mechanically damage the organic EL element, too.